I'm not sure when M60 started using PC2700. Anyway, PC2700 will work, but it will clock down to PC2100 if your mobo or BIOS don't support it, or if you use another PC2100 chip together with a PC2700 chip. Check what you are using right now.
Yes, Crucial is 50% more expensive in this case. On the other hand, there are no free lunches: rightly or wrongly, Micron has better reputation than Swissbit, and MemoryX's confusing info on Micron/Swissbit looks a bit suspect. I am not saying that Swissbit will not work for you (hopefully it will), but you should recognize that few users select memory based on prices alone.